Apparatus for aerating liquids



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H. T. JEFFERY l APPARATUS FOR AERATING LIQUIDS wwwm .A

Feb. 6, 1951 Filed oet. 4, 1946 JZfnq/e.

H. T. JEFFERY APPARATUS FOR AERATING LIQUIDS Nm, @@QN Sw mw uw Feb. 6, 1951 Filed oct. 4, 194e Patented Feb. 6, 1951 .UNITED 'STATES fPATENT` OFFICE APPARATUS FOR AERATING LIQUIDS Harold T. J eery, Wilmette, Ill., assignorto Yeomans Brothers Company, Chicago, Ill., a corporation of Delaware Application October 4, 1946, Serial No. 701,335

One. of :the most important steps in the disposal fof sewage ,is the `aeration of the various liquid and suspendedosolid components of the sewage `by diffusion, agitatonor other-.procedures, to

encourage the` growth of aerobic bacteria with,l

mthepresultant nitrilicaton and oxidation of the vwaste materials. -lThe present 'systems of aeration by diffusion utilize porous plate ortuhe struc- ;turesandgairis forced `therethrough by suitable n; pumps. orpcompressors. These systems are not wholly satisfactorybeca-use of the inherent high power demands of` the pumping eouipment and the relatively jshort lifel-of the diiiusion plates ortubes, with attendanthigh maintenance costs.

V4'il-Iowever; the-'systems provide underwater ulcera-` `Lotion of `the air and accomplish very efcient aeracton of the liquid being treated.

` Theobject of Vthepresent invention is to pror"vide an `improved tank aerating device Aoperalole to eiect underwater aeration of sewageV or other liquidsheing treated -by introducing therein nely fdivided` air4 bubbles similar-to the known underwater diffusion systems, but with greatly dencreased :power` consumptions and ,lowera main- ;tenance costs. sibleanaerating systemv with all the advantages `of `the l 4known runderwater diiusion systems but Withoutfthe disadvantages ofasuch systems. An- -fvother` "object-v off the invention isto. provide `an aeration device .in-accordance with `the above `stated fprincipal` object` which can. be -installed .1a-inw conventional diffusion aeration tanks without ".ifsubstantial' modification'` thereof. `-Furtl'ieryobjects:v and advantages ofthe Vinvention lwill be |`understood byreference to' thefollowing speci- .fiicationsk with the` accompanying drawings.

In the drawings: gl-Figi 1 isa Vsectionalaside,elevationalrview of .a fijan. aerationdevice :in accordance with fthe, invenf tion; installed in a conventionalpconcrete. @tank J vlgs212; 3 and 4 are-end elevational views, par- Mtially-in section, of typical installations'of the i, aeration devices of the invention;

"Fig- 5 is a-side elevationview; partially insec- VTT tion; jofg-an impeller suitable forusein `the aeration devices of the invention;

Fig. l6gis an end elevational view` of the im- Y :.fpeller illustrated in Fig. 5;

f t Figi. 'lis avsectional .viem-onfthe,.generaLline The invention :thus makes pos- Fig 8 is a Vsectional view` on the generalline V8 8 of Fig. l.

Theaeration device ofthe presentA invention comprises a hollow shaft having mounted thereon a Aplurality of impellers orV diffusers. Means is provided forrotating thelshaft and the impellers,

and the hollow portion-of the shaft is connected through suitable conducting `means to the at- The impellers eachcontain a plurality of` air, passageways which are in communication atthe hub of the impeller-with the hollow portion of the shaft and` extend.outward from the hub to a notch-orrecesspin.the peripheryof Y the impeller.

uWhen the shaft and its attached rotors of `the aerating deviceare rotated .by the source of power, the notches in the periphery of the individual. mpellers ,passing through the substan- `tiallypopuiescent liquid, causes asuction or aspirating effect. This acts to `draw air from the hollow shaft,l throught'ne arnpassagewaysin the iml pellers, anddischarges thatair inan attenuated stream ofsmall sized bubbles into the surrounding liquid. lThe-required rate of rotation to effeet. aeration depends chieiiy uponthe diameter rof the rotors and the head of liquid to be overcome,` and-to alesser extent upon the design of the, impeller units.

Fig. 1 shows` the installation of a rotary air .diffuser in accordance with the inventionin an ,aerating ,tank Il of `the-typeusually employedin theactvated sludge process. The.tank l t is of l,concrete construction and maysbeirom about 12 to 20 feet deep and` about 60350 120 feet in length.

The hollow shaftr I3` in this installation is rotatablymounted in suitable bearings ,I5 which .pling.25.

`Upon rotation the individual impellers draw air from the hollow shaft 13, as heretofore described, said air being conveniently supplied from suitable connections at some of the bearings l5. The cross section of a typical air supplying bearing lila is shown in Fig. 7. Thebearing IEa conl tains. an annular groove 2l' which is coincident A shaft.l3. 4 Air ilows to. the annular groove 2l 1from.

the-atmosphere through an air inlet pipeline 3i which extends above the surface of the liquid in the tank and terminates in a U connection 33 designed to exclude trash and other foreign material from the air intake pipeline 3l. Sleeve bearing inserts 35 are provided to effect the support of the shaft i3. Other bearings such as roller-bearings may be provided to effect a reduction in the frictional losses. Liquid is excluded from the air passageways during operation, and from the bearing surfaces at all times by the packing glands 31 and the packing 39 and lill. The packing 39 and 4t also serves to exclude abrasive materials from the bearing surfaces and increases the life of the bearing surfaces. It may be found desirable, depending upon the installation, to provide auxiliary supporting bearings at various positions along the shaft and to provide separate air intake bearings which have but little supporting action.

In the illustrated embodiment of the invention the impellers il are disc-shaped, as shown in Figs. and 6, enabling them to be rotated in the liquid without excessive friction losses. The disc-shaped impellers, each containing a pair of diametrically opposed, radially extending, airY passageways 4i, may be milled from a metal casting, molded from plastic, or fabricated from other materials by methods known Vto the art. Each of the discs ll is adapted to be mounted upon the shaft i3 by rneans of a key d2. .which engages the keyway 43, and a set screw d5 which ts in a tapped hole in the impeller hub d?. The impellers Il are mounted on the shaft it over slots 4l! provided in the shaft to allow the free passage of air to the air passageways in the rotor. The joint around the hub should be wiped with lead, solder, or other sealing substance to insure an airtight bond between the inner surface of the hub 4'! and the outer surface of the shaft. The air passageways il in the impeller terminate at their outer ends 48 in the notches or recesses 49 on the periphery of the disc.

The shaft I3 and impeller discs ll are rotated as a unit in the direction shown by arrow. 5l.

The passage of the notches 49 through the surrounding liquid acts to cause a suction or aspirating effect at the mouth of each of the air passageways 48. When the peripheral speedof the notch 49 is increased to a speed which will cause the pressure produced by aspirating effect to equal the pressure due to the head of the liquid in the tank, air will be drawn from the atmosphere through the pipeline El to the bearing through the hollow shaft i3, and then through the air passageways d! in therotors Il. Asl the Y air is drawn to the mouths of the air passageways at 48 the turbulentieddy currents in the liquid, caused by the movement of notch 4Q,

.effectively break the air into an attenuated stream of small diameter bubbles.

My investigations have shown that an impe]NV ler which has a diameter of 24 inches should be rotated at about 290 R. P. M. to overcome a 16 foot head of water so as to effect aeration. If `the diameter is increased to 36 inches, the rate of rotation may be reduced to about 192 R. P. M. to effect aeration in an identical tank.

The design of the impellers for my aeration device is not limited to the embodiment shown in the drawings. The impellers should be so shaped as to require a minimum of power to be l expended in their rotation. The impellers may be made with a plurality of arms which contain air'passageways withthe mouths of said pas'- liid,

lit into the liquid.

The rotating diffuser units may be installed in the conventional aerating tanks that are now in vogue to obtain the various desired convection flow patterns.V The arrows 52, Fig'. 2, show the conventional single spiral convection flow that is obtained by installing the rotating diffuser unit Eli at the base of one wall of the tank Il. It has been determined by rny investigations that a large portion of the effective aeration and the resultant reduction in the biologic oxygen demand (B. O. D.) occurs when the liquid circulates across the air-liquid interface at the surface of the tank. One of the reasons for the eicient operation of the rotary air diffuser is that Ytne circulation in the tank is materially increased by the liquid which rotates sympathetically with the rotating unit because of fluid friction. Thus, a large part of the frictional loss in the system is used to increase the convection currents,

somewhat above the bottom of the tank if@ asis shown in Fig. 4. An insallation of this type results in a decrease in the head ofliquid to be overcome with the resulting decrease in rate of rotation and power needed to rotate the air diffuser unit without resulting ina proportional decrease in aerating effect. The optimum distance from the bottoni of the tank Vvaries with the B. O, D. Yof the liquid, but in an Vordinary disposal system, with tanks about 16 feet deep, the rotating diuser unit could be advantageously located approximately two feet above the level of the bottom.

A double spiral convection flow is shown in Fig. 3. Upon aeration the air rises from the air diffuser unit 56 and tends to raise the liquid along with it. Upon reaching Vthe surface the liquid separates and flows to the outer walls of the tank I6, thus effecting double spiral flow as is shown by the arrows 53. The double spiral ow is advantageous where wide aeration tanks are installed as it insures that liquid is moving across the entire surface of the air-liquid boundary and Vresults in more efficient aeration of the liquid. f.

A conventional stuffing box, as illustrated at 51 in Fig. 8, must be provided at the point where the shaft enters the tank. The stuffing box 51 is sealed into the concrete wall of tank 'l I g and is provided with the packing filled chamber 5B and a sleeve bearing insert 58. The packing gland 6I is adaptable to compress the packing in the chamber 5S by pressure exerted upon the bearing 58. A stuiing box of the type described excludes liquid from the bearing 58 and the sump 63 and facilitates adjustment of the packing gland 5l while Y the air diffuser is operating. Y

In an exemplary sewage treatment plant'designed to treat-a million gallons of'sewage per day with an average B. O. D. contentof 200 lparts per million (P. P. Ml), about '700,000 cubic feet of andorra i fi-ee'jaii required-t0 reduce" theB'Ol! D. con- ""tent*td-a safe" value. )Thisfvolume u fairlfcanbe Vi"supplied by "the "usefofl av` 1dilfuser unit: Vin accordafloat/Vith the invention having about 60 impellers 516'feetfcieepA and' '120A feet iniengthgltne rotors hev- "fin'g eli-"diameter4 of '24 inches, and rotating at^290 Y R. y:P Tests have shown? that an averageof 41one-sixthhorsepower is `-re'quiredfor 'every Virnp'elle'rfthe unit; 'thereforei only `ten lho'rsfepower lof `'arerequired-tddiffuse this volume of air into fthe "liquid @If the `4`same volume of -airfwas fsupi plied by a' standard airi compressorj wuld'b'e neededtofurnish the required quantities of air. In `disposal systems of similar capacity wherein thesewa'ge'coinponents are aerated by nie'c'hanicalfmfeans,l such; as sprays andl rotating agitators, even more power isreduiredandless efficient aeration may result.

An aerationsystem'of the classdescribed can A be advantageously in the aeration of drinkt ving `iivater.` The smallamount of power required `arid fthe'fsimplemechanical reduirementsfof the 25 L" diffuser unit-make it ideali -forinstallatiohsthat r designed to aerate thewater in largeY tanks. 'lvlanyf aeration i devices -for water 'purification deend uponan airslcompressor i asA their source of W air andithere is some danger in such casesv effinclusion of compressor cylinder oil in the air that is passed through the water with the resulting undesirable taste characteristics.

The most important advantages of the invention are low operating costs and low maintenance cost with high eil'iciency aeration. As heretofore stated, the power requirements of the system are about one-third of the requirements of other known aeration systems. The air passages in the impellers and hollow shaft are large enough 40 that they will rarely become clogged if sewage is allowed to back up into the diffuser when the diffusers move below the critical rate. If clogging does occur, the lines may be cleared by connecting a compressed air line to the riser pipelines 3l and passing surges of compressed air through the diffuser unit while it is rotating. The rotary air diffuser eliminates the possibility of the introduction of oil and other foreign materials into the pipelines and liquid. Rotary systems of this type require no standby power as they are not damaged by accidental stoppages.

The features of my invention that I believe to be new are expressly set forth in the following claims.

I claim the following as my invention:

1. In combination in apparatus of the class described, an elongated, horizontally disposed tank having side and bottom walls for containing a body of liquid or semi-liquid material which is to be treated, and a submerged air diffusion means which extends longitudinally of said tank and which is positioned adjacent the bottom wall thereof, said air diffusion means including a plu- 55 rality of spaced apart bearings, a horizontally disposed, hollow shaft journalled in said bearings, a plurality of air diffusion impeller discs supported upon said shaft at spaced intervals for rotation in planes normal to the axis of said shaft, each of said impellers having a plurality of outwardly extending air passageways, each of which is open at the periphery of said disc to the material contained in said tank and each of which connects at the other end thereof with the interior of said pellers will causeair to iiowfthrough said con- "duitineang into and through A'said shaft, `and "thence-vial the said passagewaysfwitnin` said impe'llerdiscsinto said'fmaterial, said -source `of fhllowffshaft, conduit .means for admittingwairi at *atmospheric pressurel tofthe'interior of'saidholl'owsha'ftyfand aJsource offpower 'forrotatingxsaid fair diffuser unitair/hereby` the rotation' of fsaidl imaildpratinginanaerationtanlr whichisfabout i Poweribeingfoperablelto rotate' said diffu-ser` unit at such speedthatthe air flowing into said material* is lirithe-form `of Jattenuated streams i of small diameter bubbles, which are of such-dimen- "s'ions'th'at said streams 0f bubbles 1in ascending through saidlmaterial produce circulating `curmedia'," ati i least a i" thirty-inve horsepower f m'otor 15 rentsin-the -bodyof material contained inlsaid tank, f which` currents uflow -across i the --surface of 'i `said *body Yof material.

havinglsideand bottoni walls for Containing-1a 11 body ofliduid` ory semi-li`quid material requiring aeration'fand ciricu-lationpand aeration means for 'effecting thef aeration and circulation 'of said *liquidi4 saidimeans being operable to provide withinsaid-tank`l` attenuated streams of small diamtank; `which then flowa'cross at least a portion fof fthe `surfaceof 'the' liquid in ythetank,r andwhich finally descend to the bottom of the tank, said aeration means comprising a submerged, rotat able air diffuser unit which is located adjacent the bottom wall of said tank, and a source of power for rotating said unit, said diffuser unit including bearing supports, a horizontally disposed, hollow shaft journalled in said supports, a plurality of air diffusion impeller discs supported at spaced intervals upon said shaft for rotation in planes normal to the axis of said shaft, each of said discs being provided with at least one outwardly extending air-discharge passageway which is open at the outer periphery of said disc to the material to be aerated and each of which connects at the inner end thereof with the interior of said hollow shaft, and means for freely admitting air from the atmosphere to the interior of said hollow shaft through at least some of said bearing supports of said shaft, said diiuser unit being positioned along the bottom of said tank, longitudinally thereof, below the region in which upwardly flowing currents of liquid are required. l

3. In combination in a system of the class described, an elongated, horizontally disposed tank having side and bottom walls for containing a liquid or semi-liquid material which is to be treated, a submerged, rotatable air diffuser unit extending longitudinally of said tank adjacent the bottom wall thereof, and a source of power for rotating said diffuser unit, said diffuser unit comprising a plurality of spaced apart bearings, a horizontally disposed, hollow shaft journalled in said bearings, a plurality of spaced apart air diffusion impeller discs supported upon said shaft for rotation in planes normal to the axis of said shaft, each of said discs having a plurality of outwardly extending air passageways, each of which is open at the periphery of said disc to the material to be treated andeach of which connects at the other end thereof with the interior of said hollow shaft, at least some of said shaft bearings having annular grooves which communicate with the interior of said hollow 7 shaft by means of slots provided in said shaft, and conduit means connecting said annular grooves with the atmosphere whereby the rotation of said impellers will cause air to flow through said conduit means, into and through said hollow shaft and thence via the said passageways within said impeller discs into said Y material, and said source of power being operable to rotate said diffuser unit at such speed that the air flowing into said material is in the form of attenuated streams of small diameter bubbles.

4. In combination in apparatus of the class described, an elongated, horizontally disposed tankV havingV side and `bottom walls for containing a body of liquid or semi-liquid material which is to be treated, and a submerged air diffusion means which extends longitudinally of said tank and which is positioned adjacent the bottom wall thereof, said air diffusion means including a plurality of spaced apart bearings, a horizontally disposed, hollow shaft journalled in said bearings, a plurality of air diffusion impellerY discs supported upon said shaft at spaced intervals for rotation in planes normal to the axis of said shaft, each of said impellers having at least one outwardly extending air passageway which is open at theV periphery of said disc to the material contained in said tank and which connects at the other end thereof with the interior of said hollow shaft, conduit means for admitting air to Vwhich are of such dimensions that said streams Vof bubbles in ascending through said material produce circulating currents in the body of material contained in said tank, Vwhich currents ow across the surface of said body of material.

Y HAROLD T, JEFFERY..

REFERENCES CITED The following'references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Y Date 94,730 Field Sept. 14, 1869 1,341,024 VSeale et al May 25, 1920 1,583,591 Greenawalt May 4, 1926 1,925,777 Sperling Sept. 5, 1933 1,988,351 Fairchild Jan. 15, 1935 2,187,746 Lefevre Jan. 23, 1940 2,212,841

Maxwell Aug. 27, 1940 

